Osteosarcomas are a class of cancer originating from the bone, mainly affecting children or young adults. Prior to the 1970s, amputation was the sole means of treatment available. Amputation results in poor outcomes for patients in terms of quality of life and accordingly current trends are directed toward trying to salvage the affected limb while resecting the tumour in its entirety to reduce the risk of local recurrence and to maximise the prospects of survival. Once the tumour is resected, further surgery is typically required to reconstruct the limb.
Efforts to salvage the limb often involve the insertion of orthopaedic implants to reconstruct the bone or replacement of natural joints with prosthesis. Conventional orthopaedic implants generally have a solid construction intended to structurally stabilise the resected bone to which they are attached. To stabilise small tumour resections, solid metallic plate type implants may be fixed to the bone tissue using multiple screws. These implants are available in standard shapes and sizes and the surgeon usually adjusts the implant contour to align with the bone during surgery using trial and error. For tumours located near joints, a total joint replacement prosthesis is used. These implants are substantial in design to improve fatigue life and accordingly require significant removal of bone tissue from the affected as well as the unaffected region to accommodate the prosthesis. In the case of young patients whose bones have not matured, an expandable prosthesis may be used requiring repeat visits to biomechanics laboratories for lengthening. Once the bones reach maturity the expandable prosthesis is replaced with permanent joint replacement prosthesis, resulting in further surgery and rehabilitation for the patient. For elderly patients, the chances of prosthesis failure are greater, due to reduced physical activity and other age related complications such as osteoporosis. Moreover, the placement strategy for such prosthesis tends to focus on the configuration of the standard orthopaedic implant and how the existing bone needs to be shaped to conform to the implant, rather than focusing on the anatomical function of the bone and what is required to maintain optimal biomechanical function of the limb.
The disparity in stiffness between the existing bone and the orthopaedic implant can lead to bone resorption and subsequent loosening of the orthopaedic implant. While in some cases, conventional orthopaedic implants do provide a satisfactory result that allow the patient to return to an active lifestyle, in others, use conventional orthopaedic implants has resulted in extended rehabilitation, pain, discomfort, and lack of mobility. Therefore, there is need for the development of customised orthopaedic implants that are optimised to loading conditions of the affected region, are affordable and can be rapidly produced.
It would therefore be desirable to be able to design and manufacture an orthopaedic implant which is customised for a patient and specific to a diseased skeletal element. In particular, it would be desirable to be able to automate design of orthopaedic implants which offer a suitable compromise to the bone's inherent biomechanical function and enhance bone in-growth rate. Finally, it would be desirable to optimise the entire process of designing and manufacturing customised orthopaedic implants to enable orthopaedic implant design, manufacture and placement to take place within the time constraints of surgery.